This application is a 371 of PCT/EP99/04589, field Jul. 2, 1999
1. Field of the Invention
The present invention relates to a method of making aqueous emulsions or suspensions and, more particularly, to a method of making aqueous emulsion or suspensions with a homogenizer of the rotor/stator type.
2. Description of the Related Art
Disperse preparations of the emulsion or suspension type play a prominent role in the preparation of cosmetics, pharmaceutical products and foods. The optimization of the production process, especially with regard to saving time and energy, is therefore of particular importance. A review of modern methods of producing semisolid and liquid emulsions is given in the article in Sxc3x96FW-Journal, volume 124, 5/98, pages 308 to 313, as well as in the article in Sxc3x96FW-Journal, volume 118, 5/92, pages 287 to 296. With regard to the temperatures at which they are carried out, the methods can be divided into hot/hot, hot/cold and cold/cold methods.
The standard method of preparing emulsions is the hot/hot method, in which the fatty phase is heated to about 75xc2x0 C. and combined with the water phase, which has also been heated to about 75xc2x0 C. Subsequently, the excess energy, which was supplied in the form of heat, is removed with the expenditure of much time. This method is therefore very time-consuming and cost-intensive.
In order to reduce the energy consumption and shorten the production time, so-called hot/cold and cold/cold methods have been developed. However, these methods have the disadvantage that they are tied to certain conditions and their applicability is therefore very limited and not usable for all emulsions and dispersions. For the hot/cold method, for example, the hot oil phase is added to the emulsifying tank and water, which has not been heated, is emulsified into the hot oil phase. Until now, the prerequisites for this method were a very slow addition of water to avoid crystallization by shock cooling, as well as a sufficiently high proportion of fat to prevent a drop in temperature to below the solidification point during the addition of water. This method therefore is still time consuming and, moreover, limited to emulsions with a high fat content.
The WO 95/13787 discloses that, for producing emulsions, it is possible to mix the fatty phase and the aqueous phase at ambient temperature, however, only under the condition that, first of all, a suitable emulsifier is present and, secondly, that the fatty phase is an oil of moderate polarity. For emulsifying oils with a high or low polarity at room temperature, it is necessary that additional metal soaps be present. To begin with, these metal soaps must be dissolved in the oil at elevated temperatures and subsequently cooled; this is also time-consuming and cost-intensive.
Emulsions or suspensions, produced by conventional methods, frequently also have the disadvantage that the emulsified or suspended particles have a particle size, which is not uniform enough or too large. This is associated with an effective surface area, which is too small for many applications. Moreover, the emulsion or suspension is not dispersed optimally.
It was therefore an object of the invention to make available a simplified, broadly applicable method for producing suspensions or emulsions, which is not time-consuming and cost-intensive and, at the same time, not subject to the limitations named above and does not adversely affect significantly or even improves the desired properties of the product produced.
This objective is accomplished by a method of making aqueous emulsions or suspensions, wherein
(A) a liquid phase is first added to a tank, the latter being connected to a homogenizer, which is of the rotor/stator type and has an additional connection, through which a phase, which is to be homogenized, can be added directly onto the rotor and comes into contact with the previously added phase only in the toothed rings of the homogenizer,
(B) the homogenizer is started and subsequently
(C) a second phase, which is insoluble in the previously added phase and is to be homogenized, is supplied in liquid form over the additional connection of the homogenizer,
xe2x80x83at least one of the two phases being an aqueous phase and at least one of the two phases not being heated.
The aqueous phase can either be added first, in which case the water-insoluble phase is supplied over the additional connection of the homogenizer, or the aqueous phase is supplied to a water-insoluble phase, which has been added previously to the tank.
The concept, xe2x80x9caqueous phasexe2x80x9d, comprises water as well as mixtures of water with water-soluble solvents, such as low molecular weight alcohols, for example, ethanol or isopropanol or polyols, such as ethylene glycol, diethylene glycol, butylene glycol or glycerin.
The particles, which are to be homogenized, have an optimum particle size of, for example, about 1 xcexcm, an optimum distribution in the external phase and a large effective surface. Consequently, raw material savings can be realized since the substance, which is to be homogenized, can be used in lesser amounts. The problem of the undesired crystallization processes also no longer arises.
If the phase, which is to be homogenized, exists in solid form at room temperature, it is added in the molten state. Such phases are waxes or wax-like materials, such as natural waxes, which can be regenerated (insect wax, animal wax and plant wax), fossil waxes (crude oil wax, brown coal wax, peat wax or ozokerites), synthetic waxes (Fischer-Tropsch wax, polyethylene wax or amide wax), higher melting paraffins, esters, fats, long-chain carboxylic acids or long-chain alcohols, each having a melting or solidifying point above room temperature.
The temperatures of the previously added phase and of the melt supplied ideally are selected so that the resulting temperature of the mixture is below the crystallization or solidification point of the substance, which is to be homogenized into the previously added phase. For example, if the temperature of the molten wax is 70xc2x0 to 90xc2x0 C. and the temperature of the previously added aqueous phase is 10xc2x0 to 25xc2x0 C., a mixture with a temperature between 10xc2x0 and 40xc2x0 C. can be attained. The wax suspension obtained can then immediately afterwards be filled into containers, ready for use, without the need for a subsequent protracted cooling and without the danger of a subsequent time-delayed change in the viscosity or consistency, since the crystallization effects are concluded immediately.
In a special embodiment, the phase, which is to be homogenized, especially a molten wax or a melt of a substance, which has a wax-like consistency at room temperature, is homogenized without an emulsifier.
If the phase, which is to be homogenized, is a liquid at room temperature, it is preferably added without being heated. Such a phase may be an oil or an oil-like material, such as naturally occurring oils (vegetable or animal fatty oils), which can be regenerated, synthetic oils, silicone oils, mineral oils, essential oils, water-insoluble, branched or linear aliphatic hydrocarbons, linear or branched alcohols, especially fatty alcohols as well as long-chain ethers or esters. Suitable hydrocarbons are, for example, liquid paraffins, squalane or squalane. Furthermore, esters of trihydric and multihydric alcohols, especially vegetable triglycerides, such as olive oil, almond oil, peanut oil, sunflower oil as well as synthetic triglycerides, such as C8 to C10 fatty acid triglycerides or also jojoba oil, are suitable.
Furthermore, monoesters or diesters of the formula R1xe2x80x94COOR2, R1xe2x80x94COO-R3xe2x80x94OOCR1 and R2COO-R3xe2x80x94OOCR2, in which R1 represents a C8 to C22 alkyl group, R2 a C3 to C22 alkyl group and R3 a C2 to C16 alkylene group, are suitable as substance, which is to be homogenized. Naturally occurring monoester mixtures and wax ester mixtures, such as those present in jojoba oil or sperm oils, and branched primary alcohols, such as those known under the name of Guerbetal alcohols, are also suitable.
In addition, materials, which are usually used as opacifying agents in cosmetic materials, are suitable as substances, which are to be homogenized. These are, in particular, those having the formula R1xe2x80x94COOxe2x80x94(CHR4CHR5O)nxe2x80x94COR6, wherein R1 represents a C8 to C22 alkyl group, R4 and R5 represent hydrogen or methyl and R6 represents hydrogen or R1 and n is a number between 1 and 12 and preferably 1, 2, 3 or 4. Diesters of glycol and fatty acids are preferred.
If the hydrophobic substance, which is to be homogenized, is a liquid at room temperature, it is particularly advantageous and saves time and energy, if neither of the phases is heated (cold/cold emulsification). A special embodiment of the invention therefore is a method for producing aqueous emulsions or suspensions of hydrophobic materials, which are liquid at room temperature, for which method
(A) a liquid phase is added to a tank, the latter being connected to a homogenizer of the rotor/stator type and having an additional connection, through which a phase, which is to be homogenized, can be added directly onto the rotor and comes into contact with the previously added phase only in the toothed rings of the homogenizer, and subsequently
(B) a second phase, which is insoluble in the previously added phase and is to be homogenized, is supplied in liquid form over the additional connection of the homogenizer,
xe2x80x83one of the two phases being an aqueous phase and the other phase a hydrophobic phase and neither of the two phases being heated.
The amount of substance to be homogenized, as a proportion of the finished emulsion or suspension, depends on the requirements of the end product that is to be produced. For example, for the treatment of hair, it may amount to 2 to 10% by weight or, for creams, such as hair dyes, it may even amount to about 50% by weight
The homogenizer, which is to be used, is an essential part of the method. It is of the rotor/stator type and has an additional connection at a very specific position. Conventional, rotor/stator homogenizers are described, for example, in Andreas Domsch, xe2x80x9cDie kosmetischen Prxc3xa4paratexe2x80x9d (The Cosmetic Preparations), volume III, 4th edition, pages 305 to 307, as well as in the article in Seifen-xc3x96le-Fette-Wachse, volume 112, 1986, pages 532 to 536. The rotor stator principle is the most frequently employed homogenizing method for making cosmetic preparations. For this method, the material, which is to be homogenized, is moved by means of a rotating part, the rotor, through a stationary part, the stator. Between the rotor and the stator, there is only an extremely small gap. The homogenization effect is based on the turbulences occurring in the shear gap. When conventional homogenizers are used without an additional connection, the substance to be homogenized is already in contact with the aqueous phase and is thus present as a pre-mixture or a pre-emulsion. With these conventional homogenizers, emulsions can be produced only according to the conventional methods, but not according to the inventive method. According to the inventive method, contact between the substance to be homogenized and the previously added phase before the actual homogenization is to be avoided.